The present invention relates to a technology for enhancing the accuracy of formation of magnetization patterns recorded on a recording medium in a head system including magnetic heads and a recording and reproduction system using the head system.
As a recording and reproduction system capable of recording and reproducing desired information on a tape form recording medium, such as a magnetic tape, there have been known tape recorders (VTR, DAT, etc.) for recording and reproducing video signals and audio signals, tape streamers (or data recorders) for processing of data, and the like, in which a rotary head system (so-called rotary drum system) including magnetic heads and a rotary transformer is used.
In rotary magnetic recording by a helical scan system, where azimuth recording on a magnetic tape is assumed, the use of recording heads having gaps differing in azimuth angle makes it possible to reduce crosstalk between adjacent recording tracks by utilizing azimuth loss. For example, in a configuration using a rotary head system on which four recording heads, i.e., two + (positive direction) azimuth recording heads (hereinafter referred to as “A1” and “A2”) and two − (negative direction) azimuth recording heads (hereinafter referred to as “B1” and “B2”) are mounted, in the case where the recording heads are disposed with a predetermined angular interval (for example, 90°) around the center axis of rotation of a rotary drum, magnetization patterns on the magnetic tape are sequentially formed by the recording heads in the rotation direction of the rotary drum. That is, the magnetization patterns on the tape are sequentially recorded by the recording heads as inclined tracks extending in the skew direction relative to the tape feeding direction (see, for example, Japanese Patent Laid-open No. Hei 9-245394 (FIGS. 5 and 20)).
FIG. 8 shows schematically the formation of magnetization patterns on a tape, in which the track formation direction is set on the axis of abscissas and recording heads are disposed in the order of A1, B1, A2, and B2 along the rotation direction of a rotary drum.
As shown in the figure, the recording heads A1 and A2 have + azimuth magnetic gaps, while the recording heads B1 and B2 have − azimuth magnetic gaps. A magnetization pattern MP(A1) is formed by the recording head A1, a magnetization pattern MP(B1) is formed next to the magnetization pattern MP(A1) by the recording head B1, then a magnetization pattern MP(A2) is formed by the recording head A2, and thereafter a magnetization pattern MP(B2) is formed by the recording head B2.
Incidentally, the hatching (slant lines) shown in each magnetization pattern indicates, by the difference in its direction, a difference in azimuth angle pertaining to the recording heads. In this figure, in the vertical direction orthogonal to the formation direction of each magnetization pattern, the direction from the lower side toward the upper side in the figure is the time lapse direction, and, in the same magnetization pattern, the direction from the left side toward the right side in the horizontal direction in the figure is the time lapse direction.
Therefore, MP(A1), MP(B1), MP(A2) and MP(B2) are recorded on an overwriting mode sequentially from the lower side toward the upper side in the figure according to time series, resulting in the formation of magnetization patterns as shown in FIG. 8 on the tape.
In this case, the relative heights of the recording heads are so set that the widths (hereinafter referred to as “Tp”) of the magnetization patterns (or record patterns) required can be obtained.
Attendant on the rotation of the rotary drum, data are recorded in the order of the recording heads A1, B1, A2 and B2. After one rotation of the rotary drum, data are sequentially recorded in the order of the recording heads A1, B1 . . . in the same manner as above, whereby a series of signal patterns composed of inclined tracks are formed.
Incidentally, the value of head width (hereinafter referred to “Tw”) of each recording head is set to be greater than the required width “Tp”. This ensures that, for example, a record portion corresponding to an end portion (an upper portion of FIG. 8) in the head width direction of the recording head A1 is overwritten by an end portion (a lower portion of FIG. 8) in the head width direction of the recording head B1, resulting in the formation of magnetization patterns with the required Tp values.
However, in the conventional configuration, it is difficult to enhance the accuracy of the magnetization pattern width on the tape.
The required width Tp varies under the influences of dispersion of relative heights of the recording heads, periodic or non-periodic oscillation in the vertical direction (rotation axis direction) at the time of rotation of the rotary drum, rotational jitter, etc.
In the examples shown in FIG. 8, in the setting of Tp=5 (unit: μm), the relative height of the recording head B1 has been set off by 1 μm to the lower side in the figure in relation to an ideal position (height) for the recording head, and the relative height of the recording head B2 has been set off by 1.5 μm to the upper side in the figure.
Specifically, in this case, the Tp values (unit: μm) for the recording heads are as follows:
Recording head A1: Tp=4 (=5−1)
Recording head B1: Tp=6 (=5+1)
Recording head A2: Tp=6.5 (=5+1.5)
Recording head B2: Tp=3.5 (=5−1.5)
Where the relative heights of the heads have thus been set off, dispersion in relation to the ideal Tp values would be enlarged.
As a countermeasure against the above problem, it is necessary to suppress the dispersion of the relative heights of the recording heads. Since the recording heads are formed of a metallic material, however, there arise the influences of temperature change and the change with time of the metallic material and the like, so that it is practically impossible to eliminate the dispersion of heights completely. In addition, as for causes of other variation (for example, periodic or non-periodic oscillation in the vertical direction at the time of rotation of the drum, rotational jitter, etc.), there is a certain limit to the preclusion of the influences of the causes of variation (for example, in the present status, the total variation amount of Tp values can be suppressed only to about 1 μm, or a high cost would be required to obtain a higher accuracy).
Incidentally, in the above-mentioned case, as for the accuracy of Tp values, there arises a dispersion of about ±1 μm for Tp=5 μm, i.e., −1 μm for 5 μm (that is, 4 μm); when reduced to record signal level, this dispersion corresponds to a lowering in S/N (signal to noise) ratio by about 2 dB (≈20·log(4/5)). Particularly, the influence increases in the case of small Tp values.